Air conditioning systems are often installed in motor vehicles to improve driver and passenger comfort. Typical air conditioning systems comprise elements of a refrigeration system which include a compressor driven by the engine, a condenser, an expansion valve, an evaporator and an accumulator. A blower is provided to blow air over the evaporator and the cooled air is directed into the interior of the vehicle.
When the air conditioning system is operational, it is recommended that the windows, doors and other openings such as sunroofs of the vehicle are closed to isolate the interior of the vehicle from the hotter air outside and reduce the heat load on the air conditioning system. However, in some military and other operational vehicles, it is necessary or desirable to maintain part of the vehicle open to the outside atmosphere. For example, some military vehicles such as tanks and HMMWVs (High Mobility Multi-Wheeled Vehicles) have an opening in the roof, known as a cupola, for accommodating an observer or gunner. The cupola may be provided with one or more vehicle mounted weapon system operated by the observer. Due to the requirement for easy access by the observer to the interior of the vehicle, the cupola remains open during operation, allowing cool air supplied from the air conditioning system to escape quickly from the interior of the vehicle.
In hot climates and without air conditioning, the temperatures inside the vehicle can reach 160° Fahrenheit (F) or more. With the air conditioning system operational, the temperature in vehicles with cupolas is reduced typically to about 110° F., which is still very hot and uncomfortable to endure for long periods of time. Furthermore, in extreme ambient temperatures, the interior of vehicles can become uncomfortably hot, even with all openings closed and the air conditioning full on. Such conditions are not safe for the occupants and may result in elevated core temperatures and harmful thermal stress to the human body.
To mitigate this problem, it has been proposed to provide each occupant of the vehicle with a cooling vest through which a liquid coolant is circulated to provide localized cooling and to maintain core body temperatures within acceptable levels.
In one personal microclimate cooling system developed for military applications, the liquid is circulated through a heat exchanger which is mounted in a cooling duct through which air from the air conditioning system is directed. After passing over the heat exchanger, the air is directed into the interior of the vehicle to provide interior cooling. A schematic of this system is shown in FIG. 1.
Referring to FIG. 1, a conventional vehicle air conditioning system comprises a compressor 5, a condenser 7, an expansion valve 9, an evaporator 11 and an accumulator 13. The evaporator is mounted in a cooling duct 15 through which air is blown to the interior of the vehicle. An air-to-liquid heat exchanger 17 is also mounted in the cooling duct and cools liquid for the cooling jackets with cool air from the evaporator. Air from the heat exchanger is subsequently expelled from the cooling duct directly into the interior of the vehicle to provide interior cooling.
A drawback of this arrangement is that the outlet temperature of liquid from the heat exchanger is typically between 75° F. and 80° F. with an air inlet temperature of 70° F. Thus, the liquid supplied to the cooling jacket for heat exchange is still relatively warm and, since heat transfer rate is dependent on temperature difference, the temperature of the liquid is too high to remove heat from the body at a sufficient rate to achieve the desired cooling and core temperatures. Conventional air conditioning systems are therefore incapable of producing sufficient cooling power to cool a microclimate system such as a liquid cooled vest. Another problem is that the air blown into the interior of the vehicle after performing heat exchange with the liquid, is warmer than normal and is therefore less effective in cooling the interior space. A further drawback is that the heat exchanger presents an impedance to the airflow, which either reduces the airflow to the vehicle interior or requires more power from the blower to maintain the airflow at the same level. Furthermore, the heat exchanger is relatively bulky and takes up a significant amount of space which is typically limited in such vehicles.
In military operations, particularly those in hot, harsh climates (e.g. in desert conditions), the availability of drinking water is essential in maintaining a proper level of hydration to prevent heat injury. Mobile patrol missions can last for extended periods of time, for example up to 18 hours or more. Thus, it is important that the vehicles are stocked before the mission with adequate supplies of drinking water. Typically, a cooler containing water bottles and ice are loaded onto a military vehicle such as a HMMWV, and additional bottles are loaded onto the vehicle and stashed in any available space. While the cooler provides an initial source of relatively cold drinking water, the temperature of the cooler will rise to ambient temperatures once the ice has melted and therefore may reach temperatures of 140° F. or more. The additional bottles stored externally of the cooler will be at similar temperatures. Water at these temperatures is not only unpalatable, but also is not absorbed by the body as easily as cooled water.